to do a full scan, with your new OBD2
USA only(Canada too)
Jeep Scans? Ford simulator scans. Jump to older OBD1 1989-95'
1996 and newer:
Just for the engine, only! (and 1997 and up adds, the 4speed transmission codes P07xx)
(OBD facts ?)
(What is this Jargon ?)
No more detractions... Below is a Real 1996 USA Tracker, (Sidekicks do same thing) All cars in the USA do this, and starting in 1998 in Canada.
The below are OBD2 SCANS ! (we invented OBD2, so....it just works here!)
What is a Monitor, or a Freeze Frame or a Pending DTC ? or A DTC? What is fuel Trim?
Conditions: Out door Temperature is 50° deg. F and was so, all night long , it's now 6 AM. ( I got out of bed ). A base line makes this topic easier !
This is a common sequence of events. That every tech witnesses.
I will start with a cold engine and show you what to look for, on the scan tools screens.
FYI: You can scan, keyon, idling , drivng , slow , fast or flogging the dog out of the car. You can not hurt the car USING THIS TOOL. (I drive and log, not look while driving)
Lets SCAN on board diagnostics: (read your manual for your tool, to connect, USB cable or , BlueTooth or wireless) (or a standalone hand tool, all ways work)
Plug in my scan tool above my right knee. Then...
I turn the Ignition key to on, the ECU Wakes up and so does my OBD2 scan tool, I can see a few things, here and now. (throttle angle works , just key on, only)
If pin 16 on the scan tool DLC port is dead, (dome fuse blown does that) the tool will NOT communicate.
The CEL lamp glows in the Instrument cluster panel .This only means the ECU thinks , it's alive.
The tool then shows me...
I see no MIL status codes, no DTCs stored. I see all Monitors are complete. (synonyms for the silly dash lamp: MIL = CEL = SES) Check engine light or service engine soon.
The dash CEL lamp is mostly useless , until it glows running, it does not tell you the ENGINE IS OK, ever.
As you can see, the Scan tool makes the CEL lamp just a toy, the tool will always work,even with a burned out CEL lamp. My tool shows no CEL acive !
If you see a CEL active, read the DTC codes now. Write them down, for later ponderments. Why do I get DTC errors?
I next, look at my (PIDS) at all sensors to see if they make sense. The first is throttle angle TPS. (PIDS are live sensor data and more)
The TPS ?, I can move the throttle, with my right foot, from Min. to Max. and the TPS, parameter (PID) shows this sensor data increases and changes. 1 for 1...
My Palmer scan software can scan relative TPS angle or Absolute (or both), depending on your tool, it may show 0, this is Relative, the ECU takes boot up absolute angle, say, 10% and subtracts, 10% from all readings for relative TPS angle. What yours does, should be obvious by it's actions. (my Palmer soft, flat tells you, which is which.)
The TPS error stated in the DTC P0122 page of 4% is the boot up absolute angle below 4% is an errror, about 0.2v is illegal TPS angle voltage. (throttle cable set too tight? oops)
KEY ON, not running.
Next, we examine the 2 temperature sensors : Key on, still not stated yet. ( Parked over night then at 6am in the morning)
When parked a long time the ECT and IAT should match , they both had all night to equalize, but on the 16v the IAT is in the Air cleaner box, it will be closer to ambients.
Both sensors are Dead cold, as it must be. (this is my first test to see if the 2 temperature sensors, read correctly not some crazy number)
The ECT coolant sensor shows the average over night air temp., plus a tad more. Say it was about 50F last night my ECT might read 60F or even 50F.
The IAT , air temperature sensor ,might read 55°F, and pretty close to the above reading given those ambient conditions. (of one read 0F or 100F, that be WRONG)
RPM is zero. sure , the engine has not been started. (engine speed)
MPH speed zero, (VSS) the car is not moving. (vehicle speed sensor) Miles per hour, is zero.
Calculated- load = 0 (yes the ECU calculates the engine load at all time, low in neutral and high up hill fast. (for sure, load never goes to zero, unless motor stalls)
Load is used for fueling, spark advance, dropping out EGR, shifting that 4speed automatic, (shift points) and even cuts out the A/C if engine load goes too high)
Spark advance, is zero, again, it is not running. The ECU only generates advance on a running engine,
and the MAF is 0 grams/per min. not running, sure, there is no air flow now. The pistons can not suck air, not running.
The above was just looking for really gross sensor errors. Some newer cars will not allow you to scan, just key on , but my 96 to 98 does.
I start the engine. veeeerrrrrrooommmmm.....
I let it idle fast, (cold runs fast) Hot is 800 RPM , no accessories on.
I immediately see, RPM goes to, say 1500 RPM cold (varies by air temps , colder faster) then slowly the RPM drops as the engine warms (IAC valve does that all by its lonesome)
RPM is just the CMP cam sender speeds. The ECU takes the Cam speed and multiplies it by 2 to get crank shaft speed.
The CEL lamp , goes OUT. this tells me, That going out means car passes smog tests in USA only, but , there can be DTC errors now. (newer the car , the more this is true)
Some codes like P0400 are hidden to the driver, in Canada. No CEL glows ! on failure. there. (the FSM book covers all these minor details, I recommend reading that)
THE AIR METER: (in this case a MASS Air Flow ) meter. (if suspect , clean it, gently with MAF cleaner by "CRC"(tm).
I notice the MAF wakes up and shows spec.1.5–4.0 grams per second , it can be more, in (Alaska) a faster RPM Imperial? 0.66–1.32 lbs. per minute
mine ,shows 1 Lb/minute air flow at idle. (my software allows grams or lbs , displayed) 1lb is good. if not , the MAF is bad.
The Manifold pressure (EGR map sensor) maybe on the display, it will show a higher pressure W.O.T. and low at idle.(it does not effect engine, its only a test sensor)
Most scan tools can not see the EGR MAP. (only factory tools and the like , high end tools)
I see spark advance at 19 Deg. BTDC. I can race the engien and get 40degree's easy.
Load is 3% in neutral idling. (A/T will be more, if in Drive) You can use Drive to raise load or change the MAF flow greatly. A/T means automatic tranny.
My car has a working 0² heater and can hit closed loop (CL) on an average day in 15 seconds flat. (longer if very cold out doors) There is a DTC for a failed heater.
My TPS shows, 10% (I am not touching the throttle pedal )
The ECT begins to warm now, as the water temperature rises . it will hit 180 to 195F , depending on the thermostat type. Once there, It must stay there running. (rare to fail)
160F is a bad thermostat (or missing or upside down or this) or ECT is bad (drifted off spec, and is bad , the ECT reads about 300 ohms on a hot enigne "unplugged" key off)
The IAT will warm to the ambient outdoor temperature, the sensor is located in the air cleaner. So, sees lots of fresh cool air... ( the IAT never fails, but does get unplugged alot.)
You must get to closed loop, by crossing about 158 F° coolant temp.'s. (ECT) ( if not big problems, bad 0²sensor or induction leaks or exhaust leaks)
The MAF responds to (5.0–10.0 grams per second) at 2,500 rpm. as you gun the engine in neutral. Up a hill it does this.(note bad coolant thermostat (slow)
Keep in mind the MAF hits max only under a full load , at W.O.T. (hills) see graphic of it here?
You can clean the MAF with CRC MAF cleaner, spray, at a distance of 6" or more.. do not touch the hot wire inside the MAF, with any object.
If in closed loop , your good, if not , you have to troubleshoot way not? (leaks in the intake? or exhaust leaks? near the front 0² sensor?)
Advanced ways and means: (ASE classes?)
On a good engine, we can see LTFT (long term fuel trim) about -5% (minus) this is a good sign for fuel trim.
We can add to inducted air some propane gas to force the 0² sensor to go leaner or richer.
Or cause illegal air leaks to force lean.
I can plot 0² sensor readings in a graph and watch ! see blue trace below? 0² means oxygen sensor front.
See the 0² hunt? below? Bottom Blue trace? It must hunt, or it's not in "closed loop".
See my pages on lean or rich here. (flooding, misfire and bogging, here)
If the 0² shows lean all the time, I look for exhaust leaks near this 0² sensor, all cracks suck air and air is 20% oxygen
and that will cause any good 0² to lie.
If you see a MAP sensor that is for the EGR only, its only used to test the EGR functions. 1996 and newer cars.
Photo's: This software is real fancy, I can plot live, and log data, on 12 sensors or Parameters. at once. Sex on wheels, no?
#1 With My Palmer OBD2 system below, I can log (record) and play back later, sitting at my desk safely, no distractions driving.
Note the MAF hitting 70 G/s ! under big load, a HILL.
I'm Driving. up to 50 MPH here. A 5sp tranny, so lots of shifting going on. ( I can look at 1 sensor or all of them, any or all PID's)
The below is me monitoring PID's (they are Parameters live from sensors or calcs.)
VSS is speed. the others should be obvious... MAF? , SHRTFT is short term fuel trim, and 02s11 is oxy sensor 1. front. Fuel_FR is injected fuel rates.
MAF is AIR FLOW. (mass airflow) (if the MAF reads low the engine WILL bog at wide open throttle) "BOG = gross lack of engine power" aka, bogs down..
Before looking at sensor data, you must know how the sensor works. (temperature, air flow, pressure, or gas flow, angles (throttle) and TRIM)
See blue trace above, that is the 0² sensor hunting , called "crosscounting". (newer sensors swing faster)
If the 0² wiggle ( stuck high? it's rich, stuck low? it's lean) if wiggling full extremes? as per above? it's STOICH (14.7:1AFR)
If say, I added extra air, to the intake (pulling the EVAP VSV hose does that) and the 0² did not move low, the 02 is bad or the injectors are way rich or leaking.
Find a vacuum hose and make a leak.
If say , I added propane gas to the air cleaner box, and it didn't move high, then the 0² is bad, or you have massive induction air leaks.
if I added air or propane and the 0² started swinging ,that is a good sign the 02 is ok. (mostly) It tells me the ECU wants to hunt it and that its in closed loop now. If the ECU is stuck in limphome it will not attempt to hunt (swing). Adding air or propane ,might end limphome !
The ECU cause the swing or hunt not the 0² That is because this sensor is a switch only. (greater than Stoich, less than Stoich, binary it is)
End Palmer data: (assumes 0² is not biased (bad)
New Scan tool , more basic. NO SEX ! Like the above.
Photos 1 to 6 Sequence from cold to hot motor. (My very old Harrison R&D unit ,circa 1996)
On this tool I can only graph 1 or 2 sensors at a time.
See dead cold rising to 120F ECT? , and hits closed loop in photo frame 6, see 1 lb/min, in frame 3 , at the MAF its all working right...
Note, that in frame 3 , closed loop hits "CL" , my fuel trim is very good at minus 2.65, the ECU IS subtracting this fuel , a very good sign for a balanced EFI.
In frame 5 see the 0² swings fast , it's just one sensor B1S1. and swings beautifully, top to bottom and fast. Bank1 sensor 1 is FRONT.
The front sensors governs fuel mix, not B1S2 that sensor is only the CAT monitor. Just ignore the B2 or S2 in frame 6. B2 is for V6/8 engines.
Full advance (in neutral , hot , doing full RPM punch outs. 3500? If you can't get to here, consider Limphome mode is TRIPPED.
Oxygen, this next plot is the 0xygen content of the exhaust stream the front OXY Sensor.
0.5 volts is perfect combustion. The toggling is the ECU hunting this perfection, over and over.
Like a man walking a tight rope. (the toggle action shows the ECU is in closed loop.)
Short and long term fuel trim uses this sensor to keep fueling perfect at all times.
The Front 0², sensor B1S1(bank 1 sensor 1) must swing and swing at idle and at cruise Hot. or you have serious air fuel issues.! etc, etc..
This is closed loop happening, the ECU is hunting Closed loop , over and over for Stoich, witch is 14.7:1 AFR, 14 parts air to 1 part fuel. (by weight)
(it is a closed loop servo action) Like a thermostat in your home heating system.(vastly faster)
The 0² is really an 0² switch, it can only say to the ECU, too rich , or too lean, and can never say, by how much?. (it's called a narrow band sensor)
The ECU and 0² have the authority to pull fuel mix 25% if it goes that far, if too far? the OBD system trips lean or rich DTC's P0171 or 172
I call this tripping the 0² rails. OBD2 also limits the injection at these rails, That way, the black cloud behind car is greatly reduced in hard failures.
The next scan tool, shows my 0² senor this way below: A pocket scan tool .
This graph, "Live Data" page is accessed by using the cursor key, highlighting the 02B1S1 (S2 is useless for trim) and pressing ENTER on the tool. Even though the data page is missing the "G" icon (for graphable) it still plots perfectly, like the below,
(This works ( I tried it) on my 96/97 and 04 trackers) for sure all 96+ it works.
This is a good 02. below: It has a full sweep, min to max.
(ignore the missing , returns to zero, it's the slow scan that misses that, only a TRUE DSO can see every peak and valley)
It must do this below at light cruise too, with a steady right FOOT.
(see this at idle, , racing in neutral and under steady load)
(the 02 drops out , accelerating or at WOT) To get good MPG, check all modes of driving and this live PLOT.
This scan tool Maxi chops up the signa,l due to its very slow scan rate (digitization), that is, fine we know it looks like photo 3 below , in reality.
Bad 02 readings below. x2 (photo 2a and 2b.)
GOOD 02 BELOW : readings at idle or light cruise (no hills) or just idle racing motor. (not at wide open throttle or accelerating or cut fuel modes of ecu)
Many good EFI systems can swing 6 times a second, for best MPG. As they age the get slow, and MPG drops.
6 corrections per second, 1 swing per second is an old tired sensor.
(they (02) have a life span of about 100k miles , no wild? addtives in fuel, or AF leaks)
200ms is 1/5 second. so this sensors swings 5 times per sec. (a fresh sensor)
Photo3: (THE REAL THING BELOW, VOLTAGE VERSUS TIME ) (not a poor digitization like the OBD2 does)
DSO means Digital Storage Oscilliscope. (any scope can do this, any made from 1950 to now. really !, even a used $50 scope)
Keep in mind, about the ECU, if it reads lean from the 0², then the ECU swings rich to correct it. The above 2 photos are of failing system , Lean then Rich.
Some times, you get a straight line on the DSO. stuck rich or lean. That is a hard failure.
I add air for rich and propane for lean, to see if I can wake it up.
MAF FACTS: The MAF is the most difficult too test. But these plots are of a GOOD MAF. Under LOAD.
The MAF usually, don't exceed, 55 gr/sec. "55 grams per second....... yes, air does have mass.
but I did a test run, in 3rd gear , (5sp) wide open throttle up a nice steep hill, trying to drain the gas tank, as fast as possible. Yes, sick I am.
Bottom axis is time, and therefor distance. A dirty MAF Hot wire, limits max power and speed, under load. Clean the MAF.
This is just fooling around. here. MPG. See I got 200MPG for an instant. No big deal and all very normal for EFI.
Last and lots of fun, I ran the MPG plot. (click it, to zoom it)
This Scan tool allows me to plot my own created parameters. MPG is comes with software.
Each time I say , x is bad, that means the wires and connectors to that object are perfectly good (conductive and insulation good)
OBD2 Monitors: (what are they?) I call this Doctor Monitor.
A monitor, is like hidden Doctor , under you engine hood, and can magically test things, as you drive.
If he see's something wrong, he turns on the CEL solid engine running, and stores a DTC code. (1 or more codes, like P0400 EGR)
The doctor will flash the CEL every 2 seconds to warn you that the CAT is melting. (way rich fuel)
OBD2 has no per se' flash codes, like OBD1, you must use a scan tool or go to Autozone and ask them to scan you.
How ever the CEL flashing in a non intelligent way means the CAT is going to burn up, the operators guide tells you what to do, "get car serviced soon"
No ECU, knows if the engine or EFI are ok. (It mostly just warns you for hard fails, or smog failing)
The scan tool allows human to see live data and now you can find lots of other evidence of problems.
For example, closed loop fails , hot idle or driving on flat ground at 40mph, steady right foot and speed, this is a failure only humans can detect (in 1996)
As is noting a weak MAF, or the ECT not matching true coolant temperatures. (and lots more)
In an OBD II system, the
following monitors are run by the PCM: